Strong evidence for a weakly oxygenated ocean–atmosphere system during the Proterozoic

The Great Oxidation Event (GOE), arguably the most important event to occur on Earth since the origin of life, marks the time when an oxygen-rich atmosphere first appeared. However, it is not known whether the change was abrupt and permanent or fitful and drawn out over tens or hundreds of millions of years. Here, we developed a one-dimensional time-dependent photochemical model to resolve time-dependent behavior of the chemically unstable transitional atmosphere as it responded to changes in biogenic forcing. When forced with step-wise changes in biogenic fluxes, transitions between anoxic and oxic atmospheres take between only 10 2 and 10 5 y. Results also suggest that O 2 between ~ 10 − 8 and ~ 10 − 4 mixing ratio is unstable to plausible atmospheric perturbations. For example, when atmospheres with these O 2 concentrations experience fractional variations in the surface CH 4 flux comparable to those caused by modern Milankovich cycling, oxygen fluctuates between anoxic ( ~ 10 − 8 ) and oxic ( ~ 10 − 4 ) mixing ratios. Overall, our simulations are consistent with possible geologic evidence of unstable atmospheric O 2 , after initial oxygenation, which could occasionally collapse from changes in biospheric or volcanic fluxes. Additionally, modeling favors mid-Proterozoic O 2 exceeding 10 − 4 to 10 − 3 mixing ratio; otherwise, O 2 would periodically fall below 10 − 7 mixing ratio, which would be inconsistent with post-GOE absence of sulfur isotope mass-independent fractionation.

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“…We conclude that, for stability, mid-Proterozoic O 2 levels should have exceeded

. This conclusion is compatible with mid-Proterozoic Fe isotopes in ironstones, which suggest O 2 levels between approximately

and

mixing ratio ( 43 ).…”

Section: Discussionsupporting

confidence: 81%

Rapid timescale for an oxic transition during the Great Oxidation Event and the instability of low atmospheric O ₂

Wogan

Catling

Zahnle

et al. 2022

Proc. Natl. Acad. Sci. U.S.A.

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“…During the majority of the Proterozoic Eon, pO2 was maintained at intermediate levels, likely ~10% PAL and possibly as low as ~1% PAL [20][21][22]131 , leaving the deep oceans predominantly anoxic 132,133 , with predominantly oxic surface waters except in (anoxic) upwelling regions 21 . Others argue for pO2 <0.1% PAL 134 or <1% PAL 135,136 during the mid-Proterozoic, which would have left a mostly anoxic surface ocean containing 'oxygen oases' near primary producers (just as prior to the GOE) 21,137 . Thus, despite an oxidising atmosphere after the GOE (ca.…”

Section: Redox Evolution Of Earth's Surface Environmentmentioning

confidence: 99%

Eukaryogenesis and oxygen in Earth history

et al. 2022

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The endosymbiotic origin of mitochondria during eukaryogenesis has long been viewed as an adaptive response to the oxygenation of Earth's surface environment, presuming a fundamentally aerobic lifestyle for the free-living bacterial ancestors of mitochondria. This oxygen-centric view has been robustly challenged by recent advances in the Earth and life sciences. While the permanent oxygenation of the atmosphere above trace concentrations is now thought to have occurred 2.22 billion years ago, large parts of the deep ocean remained anoxic until less than 0.5 billion years ago. Neither fossils nor molecular clocks correlate the origin of mitochondria, or eukaryogenesis more broadly, to either of these planetary redox transitions. Instead, mitochondria-bearing eukaryotes are consistently dated to between these two oxygenation events, during an interval of pervasive deep-sea anoxia and variable surface water oxygenation.The discovery and cultivation of the Asgard archaea has reinforced metabolic evidence that eukaryogenesis was initially mediated by syntrophic H2 exchange between an archaeal host and an ⍺-proteobacterial symbiont living under anoxia. Together, these results temporally, spatially, and metabolically decouple the earliest stages of eukaryogenesis from the oxygen content of the surface ocean and atmosphere. Rather than reflecting the ancestral metabolic state, obligate aerobiosis in eukaryotes is most likely derived, having only become globally widespread over the past half billion years or so as atmospheric oxygen reached modern levels.

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“…Life on Earth shifted from anoxia to oxygen conditions [ 22 ], evolving the respiratory systems. The increasing ROS level allowed for more complex organism development, improved body size, and biodiversity.…”

Section: Oxidative Stressmentioning

confidence: 99%

To Be or Not to Be? Are Reactive Oxygen Species, Antioxidants, and Stress Signalling Universal Determinants of Life or Death?

Szechyńska‐Hebda

Ghalami

Kamran

et al. 2022

Cells

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In the environmental and organism context, oxidative stress is complex and unavoidable. Organisms simultaneously cope with a various combination of stress factors in natural conditions. For example, excess light stress is accompanied by UV stress, heat shock stress, and/or water stress. Reactive oxygen species (ROS) and antioxidant molecules, coordinated by electrical signalling (ES), are an integral part of the stress signalling network in cells and organisms. They together regulate gene expression to redirect energy to growth, acclimation, or defence, and thereby, determine cellular stress memory and stress crosstalk. In plants, both abiotic and biotic stress increase energy quenching, photorespiration, stomatal closure, and leaf temperature, while toning down photosynthesis and transpiration. Locally applied stress induces ES, ROS, retrograde signalling, cell death, and cellular light memory, then acclimation and defence responses in the local organs, whole plant, or even plant community (systemic acquired acclimation, systemic acquired resistance, network acquired acclimation). A simplified analogy can be found in animals where diseases vs. fitness and prolonged lifespan vs. faster aging, are dependent on mitochondrial ROS production and ES, and body temperature is regulated by sweating, temperature-dependent respiration, and gene regulation. In this review, we discuss the universal features of stress factors, ES, the cellular production of ROS molecules, ROS scavengers, hormones, and other regulators that coordinate life and death.

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Strong evidence for a weakly oxygenated ocean–atmosphere system during the Proterozoic

Cited by 23 publications

References 67 publications

Rapid timescale for an oxic transition during the Great Oxidation Event and the instability of low atmospheric O ₂

Rapid timescale for an oxic transition during the Great Oxidation Event and the instability of low atmospheric O ₂

Eukaryogenesis and oxygen in Earth history

To Be or Not to Be? Are Reactive Oxygen Species, Antioxidants, and Stress Signalling Universal Determinants of Life or Death?

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Strong evidence for a weakly oxygenated ocean–atmosphere system during the Proterozoic

Cited by 23 publications

References 67 publications

Rapid timescale for an oxic transition during the Great Oxidation Event and the instability of low atmospheric O 2

Rapid timescale for an oxic transition during the Great Oxidation Event and the instability of low atmospheric O 2

Eukaryogenesis and oxygen in Earth history

To Be or Not to Be? Are Reactive Oxygen Species, Antioxidants, and Stress Signalling Universal Determinants of Life or Death?

Contact Info

Product

Resources

About

Rapid timescale for an oxic transition during the Great Oxidation Event and the instability of low atmospheric O ₂

Rapid timescale for an oxic transition during the Great Oxidation Event and the instability of low atmospheric O ₂